Detection of a molecule, e.g., a nucleic acid, a polypeptide, a carbohydrate, or a combination thereof, or binding between a molecule and a binding partner of the molecule is a common assay technique. Many molecular detection techniques are limited by low a concentration of the molecule, a relatively high concentration of similar molecules, difficulty in isolating the molecule, and similar drawbacks. As a result, many known molecular detection techniques are difficult or impossible to perform, and results obtained using such methods can be inaccurate. A drawback shared by most prior detection methods is that they require that a member of the binding pair, or the bound pair, be detectably labeled. In addition to increasing the labor requirement and complexity of the test, such labeling can interfere with the assay results.
Nanomechanical biodetection devices and methods have recently been developed by others, e.g., Fritz et al., 2000, Science 288:316–318, and do not require labeling of receptors or ligands. In prior art devices, a micrometer-scale cantilever is formed from a material that reflects light, and one member of a receptor-ligand binding pair is immobilized on a face of the cantilever. Binding of the other pair member with the immobilized pair member induces a stress on the face of the cantilever having the immobilized pair member thereon, resulting in bending of the cantilever. Bending of the cantilever is detected in prior art systems by a change in the path of light reflected off a distal portion of the cantilever.
A difficulty experienced using nanoscale cantilever-based binding detectors based on reflected light is that the devices are highly sensitive to minute vibrations. Any misalignment of the optical beam severely degrades the optical signal. Also, use of an external optical source and reader with an array of nanoscale cantilevers requires reliable and highly accurate repositioning of the light source, the detector, the array, or some combination of these. Apart from the need for precise mechanical actuators to perform those manipulations, the manipulations themselves prevent parallel real-time detection of multiple biomaterials. Prior art methods of using nanoscale cantilever microarrays also require precise positioning of optical components relative to the array.